This first step is decisive for the final welding result since the surface of the material undergoes physical transformations during welding that are sometimes sudden and that may have unforeseeable consequences for the quality of the weld obtained.
At present such processes are routinely implemented using various methods of preparing the surface of the weld region before proceeding to the welding step as such.
For example, U.S. Pat. No. 5,681,490 describes a method of monitoring the quality of a weld effected by a laser beam. To this end, the document teaches measuring and analysing the values of various physical parameters that change as welding progresses, namely the energy reflected by the surface of the material to be welded, the energy transmitted through the material, and possibly the parameters of the laser beam employed.
However, the process described in the above patent has major technical limitations. This is because the results obtained from the analyses carried out are used to constitute a database of “signatures” of welds that have been executed including the associated welding parameters, the signatures providing an indication of the level of quality of the corresponding welds. The device for implementing this process consults the database during subsequent welding operations in order to use again the welding parameters that have produced welds of good quality and to attempt to reproduce the corresponding level of quality.
A major drawback of this process results from the fact that the original surface state of the material to be welded varies unpredictably. Thus welding parameters that led to a weld of good quality for a first sample of a given material will not necessarily yield a weld of good quality for a second sample of the same material.
This is why U.S. Pat. No. 5,681,490 makes further provision for detecting the quality of a weld that has just been carried out in order to rectify it should it prove to be of poor quality. Because rectifying the weld itself is not always possible, as in the particular case of overheating leading to the formation of a hole through the material, there is provision for carrying out a new weld near the spoiled first weld.
A solution of this kind is not always acceptable in relation to the required visual appearance of the weld, in particular if it is located in a portion of the corresponding final product that is visible.